Recently, research and development of sensor networks configured with a large number of information transmitting terminals equipped with sensors has advanced. An information transmitting terminal used in such a sensor network is required to be maintenance-free, and as one problem thereof, a battery-free configuration, that is, a configuration in which the information transmitting terminal is equipped with a power supply source such as a power generator and a battery is unnecessary, is necessary.
As an example of a technique for implementing the battery free configuration, research and development of a technology called energy harvesting, that is, a technology of collecting energy, such as sunlight, illumination light, a vibration generated by a machine, or heat, and obtaining electric power therefrom is under way.